Different light. Two studies question validity of volume measures.
D000368:Aged; D006348:Cardiac Surgical Procedures / Q000401:mortality / Q000592:standards / Q000706:statistics & numerical data; D006265:Health Care Coalitions; D006302:Health Services Research / Q000379:methods* / Q000592:standards; D006761:Hospitals / Q000592:standards* / Q000706:statistics & numerical data*; D006801:Humans; D007231:Infant, Newborn; D033181:Information Dissemination; D007363:Intensive Care Units, Neonatal / Q000592:standards / Q000706:statistics & numerical data; D019984:Quality Indicators, Health Care; D015203:Reproducibility of Results; D014481:United States / Q000453:epidemiology